Recently, light emitting diodes or EL elements are mounted in various electronic apparatuses, specifically mobile terminals such as mobile phones. The light emitting diodes or EL elements emit light so as to light an operation portion such that the operation or identification of pushbutton or display sheet is easily performed even when the surrounding is dark. Further, there is demand for a movable contact element and switch which are easy to use and are inexpensive.
Such a conventional movable contact element and switch using the same will be described with reference to FIGS. 5 and 6. In the drawings, the thicknesses of layers and regions are exaggerated for clarity. FIG. 5 is a cross-sectional view of a conventional switch. FIG. 6 is an exploded perspective view of essential parts of the switch. In FIGS. 5 and 6, film-shaped light guiding sheet 1, which is optically transparent and has flexibility, has a light guiding layer 1A whose top and bottom surfaces are interposed between upper protective layer 1B and lower protective layer 1C. A plurality of movable contacts 3, which are formed in substantially a dome shape and are made of a conductive metal thin plate, are bonded to the bottom surface of light guiding sheet 1 through an adhesive (not shown). Light guiding layer 1A above movable contact 3 has a plurality of light emitting portions 1D formed in an irregular shape. In such a manner, movable contact element 4 is constructed.
Substrate 5 having a plurality of wiring patterns (not shown) formed on the top and bottom surfaces thereof has a plurality of fixed contacts 6 formed on the top surface thereof, the fixed contacts 6 being composed of circular central fixed contact 6A and U-shaped outer fixed contacts 6B surrounding central fixed contact 6A. The outer circumference of movable contact 3 is placed on outer fixed contacts 6B such that the center of the bottom surface of movable contact 3 faces central fixed contact 6A with a predetermined space provided therebetween. A plurality of light emitting elements 7 composed of light emitting diodes and so on are mounted on substrate 5 in the right side of light guiding sheet 1 such that the light emitting surfaces thereof face the right side surface of light guiding layer 1A of light guiding sheet 1. Sheet-shaped operation body 8 made of insulating resin is composed of light transmitting portion 8A and light shielding portion 8B covering the top surface of light transmitting portion 8A. On the top surface of a plurality of operation portions 8C, a display portion 8D is provided, through which light transmitting portion 8A is exposed in a character or sign shape. Pressing portion 8E projecting downward is abutted on the top surface of light guiding sheet 1 at the central portion of movable contact 3. The conventional switch is constructed in the above-described manner. The switch constructed in such a manner is mounted on the operation surface of an electronic apparatus, central fixed contact 6A or outer fixed contacts 6B and light emitting elements 7 are connected to electronic circuits (not shown) of the apparatus through wiring patterns by a connector or lead lines (not shown).
In the above-described construction, when predetermined operation portion 8C of operation body 8 is pressed downward, pressing portion 8E provided on the bottom surface of operation portion 8C presses the top surface of light guiding sheet 1. Then, light guiding sheet 1 is bent to press the substantially dome-shaped central portion of movable contact 3. When a predetermined pressing force is applied, movable contact 3 is elastically inverted downward with a click feeling such that the center of the bottom surface of movable contact 3 comes in contact with central fixed contact 6A. Then, central fixed contact 6A and outer fixed contacts 6B are electrically connected through movable contact 3.
When the pressing force applied to the operation portion 8C is released, movable contact 3 is elastically inverted upward by an elastic restoring force, and the center of the bottom surface is separated from central fixed contact 6A such that central fixed contact 6A is electrically disconnected from outer fixed contacts 6B.
Further, depending on the electrical connection and disconnection of fixed contact 6, the switching of the respective functions in the apparatus is performed. Further, when a voltage is applied to light emitting element 7 from an electric circuit of the apparatus, light emitting element 7 emits light. The light is incident on light guiding layer 1A from the right side surface of light guiding sheet 1 such that the entire body of light guiding layer 1A is lighted. The light is reflected by light emitting portions 1D within light guiding layer 1A, which are formed in an irregular shape. Further, light emitting portions 1D emit light. Then, the light passes through upper protective layer 1B so as to light display portion 8D of operation body 8 from the lower side. Therefore, even when the surrounding is dark, the display of characters or signs of operation portion 8C can be recognized, which makes it easy to perform an operation. Further, as a prior art document relating to the invention, Japanese Patent Unexamined Publication No. 2006-318905 is known.
In the conventional movable contact and the switch using the same, light from light emitting element 7 is distributed on the entire portion of light guiding layer 1A of light guiding sheet 1 such that the plurality of display portions 8D of operation portion 8 are lighted. However, light emitting portions 1D distant from light emitting element 7 become so dark that unevenness occurs in the lighting. To reduce the unevenness and perform uniform lighting, a large number of lighting elements 7 need to be disposed around light guiding sheet 1. Then, the construction of the switch becomes complicated, and the price thereof increases.